from sympy.core.add import Add
from sympy.core.compatibility import ordered
from sympy.core.function import expand_log
from sympy.core.power import Pow
from sympy.core.singleton import S
from sympy.core.symbol import Dummy
from sympy.functions.elementary.exponential import (LambertW, exp, log)
from sympy.functions.elementary.miscellaneous import root
from sympy.polys.polyroots import roots
from sympy.polys.polytools import Poly, factor
from sympy.core.function import _mexpand
from sympy.simplify.simplify import separatevars
from sympy.simplify.radsimp import collect
from sympy.simplify.simplify import powsimp
from sympy.solvers.solvers import solve, _invert
from sympy.utilities.iterables import uniq


def _filtered_gens(poly, symbol):
    """process the generators of ``poly``, returning the set of generators that
    have ``symbol``.  If there are two generators that are inverses of each other,
    prefer the one that has no denominator.

    Examples
    ========

    >>> from sympy.solvers.bivariate import _filtered_gens
    >>> from sympy import Poly, exp
    >>> from sympy.abc import x
    >>> _filtered_gens(Poly(x + 1/x + exp(x)), x)
    {x, exp(x)}

    """
    gens = {g for g in poly.gens if symbol in g.free_symbols}
    for g in list(gens):
        ag = 1/g
        if g in gens and ag in gens:
            if ag.as_numer_denom()[1] is not S.One:
                g = ag
            gens.remove(g)
    return gens


def _mostfunc(lhs, func, X=None):
    """Returns the term in lhs which contains the most of the
    func-type things e.g. log(log(x)) wins over log(x) if both terms appear.

    ``func`` can be a function (exp, log, etc...) or any other SymPy object,
    like Pow.

    If ``X`` is not ``None``, then the function returns the term composed with the
    most ``func`` having the specified variable.

    Examples
    ========

    >>> from sympy.solvers.bivariate import _mostfunc
    >>> from sympy.functions.elementary.exponential import exp
    >>> from sympy.abc import x, y
    >>> _mostfunc(exp(x) + exp(exp(x) + 2), exp)
    exp(exp(x) + 2)
    >>> _mostfunc(exp(x) + exp(exp(y) + 2), exp)
    exp(exp(y) + 2)
    >>> _mostfunc(exp(x) + exp(exp(y) + 2), exp, x)
    exp(x)
    >>> _mostfunc(x, exp, x) is None
    True
    >>> _mostfunc(exp(x) + exp(x*y), exp, x)
    exp(x)
    """
    fterms = [tmp for tmp in lhs.atoms(func) if (not X or
        X.is_Symbol and X in tmp.free_symbols or
        not X.is_Symbol and tmp.has(X))]
    if len(fterms) == 1:
        return fterms[0]
    elif fterms:
        return max(list(ordered(fterms)), key=lambda x: x.count(func))
    return None


def _linab(arg, symbol):
    """Return ``a, b, X`` assuming ``arg`` can be written as ``a*X + b``
    where ``X`` is a symbol-dependent factor and ``a`` and ``b`` are
    independent of ``symbol``.

    Examples
    ========

    >>> from sympy.functions.elementary.exponential import exp
    >>> from sympy.solvers.bivariate import _linab
    >>> from sympy.abc import x, y
    >>> from sympy import S
    >>> _linab(S(2), x)
    (2, 0, 1)
    >>> _linab(2*x, x)
    (2, 0, x)
    >>> _linab(y + y*x + 2*x, x)
    (y + 2, y, x)
    >>> _linab(3 + 2*exp(x), x)
    (2, 3, exp(x))
    """
    from sympy.core.exprtools import factor_terms
    arg = factor_terms(arg.expand())
    ind, dep = arg.as_independent(symbol)
    if arg.is_Mul and dep.is_Add:
        a, b, x = _linab(dep, symbol)
        return ind*a, ind*b, x
    if not arg.is_Add:
        b = 0
        a, x = ind, dep
    else:
        b = ind
        a, x = separatevars(dep).as_independent(symbol, as_Add=False)
    if x.could_extract_minus_sign():
        a = -a
        x = -x
    return a, b, x


def _lambert(eq, x):
    """
    Given an expression assumed to be in the form
        ``F(X, a..f) = a*log(b*X + c) + d*X + f = 0``
    where X = g(x) and x = g^-1(X), return the Lambert solution,
        ``x = g^-1(-c/b + (a/d)*W(d/(a*b)*exp(c*d/a/b)*exp(-f/a)))``.
    """
    eq = _mexpand(expand_log(eq))
    mainlog = _mostfunc(eq, log, x)
    if not mainlog:
        return []  # violated assumptions
    other = eq.subs(mainlog, 0)
    if isinstance(-other, log):
        eq = (eq - other).subs(mainlog, mainlog.args[0])
        mainlog = mainlog.args[0]
        if not isinstance(mainlog, log):
            return []  # violated assumptions
        other = -(-other).args[0]
        eq += other
    if not x in other.free_symbols:
        return [] # violated assumptions
    d, f, X2 = _linab(other, x)
    logterm = collect(eq - other, mainlog)
    a = logterm.as_coefficient(mainlog)
    if a is None or x in a.free_symbols:
        return []  # violated assumptions
    logarg = mainlog.args[0]
    b, c, X1 = _linab(logarg, x)
    if X1 != X2:
        return []  # violated assumptions

    # invert the generator X1 so we have x(u)
    u = Dummy('rhs')
    xusolns = solve(X1 - u, x)

    # There are infinitely many branches for LambertW
    # but only branches for k = -1 and 0 might be real. The k = 0
    # branch is real and the k = -1 branch is real if the LambertW argumen
    # in in range [-1/e, 0]. Since `solve` does not return infinite
    # solutions we will only include the -1 branch if it tests as real.
    # Otherwise, inclusion of any LambertW in the solution indicates to
    #  the user that there are imaginary solutions corresponding to
    # different k values.
    lambert_real_branches = [-1, 0]
    sol = []

    # solution of the given Lambert equation is like
    # sol = -c/b + (a/d)*LambertW(arg, k),
    # where arg = d/(a*b)*exp((c*d-b*f)/a/b) and k in lambert_real_branches.
    # Instead of considering the single arg, `d/(a*b)*exp((c*d-b*f)/a/b)`,
    # the individual `p` roots obtained when writing `exp((c*d-b*f)/a/b)`
    # as `exp(A/p) = exp(A)**(1/p)`, where `p` is an Integer, are used.

    # calculating args for LambertW
    num, den = ((c*d-b*f)/a/b).as_numer_denom()
    p, den = den.as_coeff_Mul()
    e = exp(num/den)
    t = Dummy('t')
    args = [d/(a*b)*t for t in roots(t**p - e, t).keys()]

    # calculating solutions from args
    for arg in args:
        for k in lambert_real_branches:
            w = LambertW(arg, k)
            if k and not w.is_real:
                continue
            rhs = -c/b + (a/d)*w

            for xu in xusolns:
                sol.append(xu.subs(u, rhs))
    return sol


def _solve_lambert(f, symbol, gens):
    """Return solution to ``f`` if it is a Lambert-type expression
    else raise NotImplementedError.

    For ``f(X, a..f) = a*log(b*X + c) + d*X - f = 0`` the solution
    for ``X`` is ``X = -c/b + (a/d)*W(d/(a*b)*exp(c*d/a/b)*exp(f/a))``.
    There are a variety of forms for `f(X, a..f)` as enumerated below:

    1a1)
      if B**B = R for R not in [0, 1] (since those cases would already
      be solved before getting here) then log of both sides gives
      log(B) + log(log(B)) = log(log(R)) and
      X = log(B), a = 1, b = 1, c = 0, d = 1, f = log(log(R))
    1a2)
      if B*(b*log(B) + c)**a = R then log of both sides gives
      log(B) + a*log(b*log(B) + c) = log(R) and
      X = log(B), d=1, f=log(R)
    1b)
      if a*log(b*B + c) + d*B = R and
      X = B, f = R
    2a)
      if (b*B + c)*exp(d*B + g) = R then log of both sides gives
      log(b*B + c) + d*B + g = log(R) and
      X = B, a = 1, f = log(R) - g
    2b)
      if g*exp(d*B + h) - b*B = c then the log form is
      log(g) + d*B + h - log(b*B + c) = 0 and
      X = B, a = -1, f = -h - log(g)
    3)
      if d*p**(a*B + g) - b*B = c then the log form is
      log(d) + (a*B + g)*log(p) - log(b*B + c) = 0 and
      X = B, a = -1, d = a*log(p), f = -log(d) - g*log(p)
    """

    def _solve_even_degree_expr(expr, t, symbol):
        """Return the unique solutions of equations derived from
        ``expr`` by replacing ``t`` with ``+/- symbol``.

        Parameters
        ==========

        expr : Expr
            The expression which includes a dummy variable t to be
            replaced with +symbol and -symbol.

        symbol : Symbol
            The symbol for which a solution is being sought.

        Returns
        =======

        List of unique solution of the two equations generated by
        replacing ``t`` with positive and negative ``symbol``.

        Notes
        =====

        If ``expr = 2*log(t) + x/2` then solutions for
        ``2*log(x) + x/2 = 0`` and ``2*log(-x) + x/2 = 0`` are
        returned by this function. Though this may seem
        counter-intuitive, one must note that the ``expr`` being
        solved here has been derived from a different expression. For
        an expression like ``eq = x**2*g(x) = 1``, if we take the
        log of both sides we obtain ``log(x**2) + log(g(x)) = 0``. If
        x is positive then this simplifies to
        ``2*log(x) + log(g(x)) = 0``; the Lambert-solving routines will
        return solutions for this, but we must also consider the
        solutions for  ``2*log(-x) + log(g(x))`` since those must also
        be a solution of ``eq`` which has the same value when the ``x``
        in ``x**2`` is negated. If `g(x)` does not have even powers of
        symbol then we don't want to replace the ``x`` there with
        ``-x``. So the role of the ``t`` in the expression received by
        this function is to mark where ``+/-x`` should be inserted
        before obtaining the Lambert solutions.

        """
        nlhs, plhs = [
            expr.xreplace({t: sgn*symbol}) for sgn in (-1, 1)]
        sols = _solve_lambert(nlhs, symbol, gens)
        if plhs != nlhs:
            sols.extend(_solve_lambert(plhs, symbol, gens))
        # uniq is needed for a case like
        # 2*log(t) - log(-z**2) + log(z + log(x) + log(z))
        # where subtituting t with +/-x gives all the same solution;
        # uniq, rather than list(set()), is used to maintain canonical
        # order
        return list(uniq(sols))

    nrhs, lhs = f.as_independent(symbol, as_Add=True)
    rhs = -nrhs

    lamcheck = [tmp for tmp in gens
                if (tmp.func in [exp, log] or
                (tmp.is_Pow and symbol in tmp.exp.free_symbols))]
    if not lamcheck:
        raise NotImplementedError()

    if lhs.is_Add or lhs.is_Mul:
        # replacing all even_degrees of symbol with dummy variable t
        # since these will need special handling; non-Add/Mul do not
        # need this handling
        t = Dummy('t', **symbol.assumptions0)
        lhs = lhs.replace(
            lambda i:  # find symbol**even
                i.is_Pow and i.base == symbol and i.exp.is_even,
            lambda i:  # replace t**even
                t**i.exp)

        if lhs.is_Add and lhs.has(t):
            t_indep = lhs.subs(t, 0)
            t_term = lhs - t_indep
            _rhs = rhs - t_indep
            if not t_term.is_Add and _rhs and not (
                    t_term.has(S.ComplexInfinity, S.NaN)):
                eq = expand_log(log(t_term) - log(_rhs))
                return _solve_even_degree_expr(eq, t, symbol)
        elif lhs.is_Mul and rhs:
            # this needs to happen whether t is present or not
            lhs = expand_log(log(lhs), force=True)
            rhs = log(rhs)
            if lhs.has(t) and lhs.is_Add:
                # it expanded from Mul to Add
                eq = lhs - rhs
                return _solve_even_degree_expr(eq, t, symbol)

        # restore symbol in lhs
        lhs = lhs.xreplace({t: symbol})

    lhs = powsimp(factor(lhs, deep=True))

    # make sure we have inverted as completely as possible
    r = Dummy()
    i, lhs = _invert(lhs - r, symbol)
    rhs = i.xreplace({r: rhs})

    # For the first forms:
    #
    # 1a1) B**B = R will arrive here as B*log(B) = log(R)
    #      lhs is Mul so take log of both sides:
    #        log(B) + log(log(B)) = log(log(R))
    # 1a2) B*(b*log(B) + c)**a = R will arrive unchanged so
    #      lhs is Mul, so take log of both sides:
    #        log(B) + a*log(b*log(B) + c) = log(R)
    # 1b) d*log(a*B + b) + c*B = R will arrive unchanged so
    #      lhs is Add, so isolate c*B and expand log of both sides:
    #        log(c) + log(B) = log(R - d*log(a*B + b))

    soln = []
    if not soln:
        mainlog = _mostfunc(lhs, log, symbol)
        if mainlog:
            if lhs.is_Mul and rhs != 0:
                soln = _lambert(log(lhs) - log(rhs), symbol)
            elif lhs.is_Add:
                other = lhs.subs(mainlog, 0)
                if other and not other.is_Add and [
                        tmp for tmp in other.atoms(Pow)
                        if symbol in tmp.free_symbols]:
                    if not rhs:
                        diff = log(other) - log(other - lhs)
                    else:
                        diff = log(lhs - other) - log(rhs - other)
                    soln = _lambert(expand_log(diff), symbol)
                else:
                    #it's ready to go
                    soln = _lambert(lhs - rhs, symbol)

    # For the next forms,
    #
    #     collect on main exp
    #     2a) (b*B + c)*exp(d*B + g) = R
    #         lhs is mul, so take log of both sides:
    #           log(b*B + c) + d*B = log(R) - g
    #     2b) g*exp(d*B + h) - b*B = R
    #         lhs is add, so add b*B to both sides,
    #         take the log of both sides and rearrange to give
    #           log(R + b*B) - d*B = log(g) + h

    if not soln:
        mainexp = _mostfunc(lhs, exp, symbol)
        if mainexp:
            lhs = collect(lhs, mainexp)
            if lhs.is_Mul and rhs != 0:
                soln = _lambert(expand_log(log(lhs) - log(rhs)), symbol)
            elif lhs.is_Add:
                # move all but mainexp-containing term to rhs
                other = lhs.subs(mainexp, 0)
                mainterm = lhs - other
                rhs = rhs - other
                if (mainterm.could_extract_minus_sign() and
                    rhs.could_extract_minus_sign()):
                    mainterm *= -1
                    rhs *= -1
                diff = log(mainterm) - log(rhs)
                soln = _lambert(expand_log(diff), symbol)

    # For the last form:
    #
    #  3) d*p**(a*B + g) - b*B = c
    #     collect on main pow, add b*B to both sides,
    #     take log of both sides and rearrange to give
    #       a*B*log(p) - log(b*B + c) = -log(d) - g*log(p)
    if not soln:
        mainpow = _mostfunc(lhs, Pow, symbol)
        if mainpow and symbol in mainpow.exp.free_symbols:
            lhs = collect(lhs, mainpow)
            if lhs.is_Mul and rhs != 0:
                # b*B = 0
                soln = _lambert(expand_log(log(lhs) - log(rhs)), symbol)
            elif lhs.is_Add:
                # move all but mainpow-containing term to rhs
                other = lhs.subs(mainpow, 0)
                mainterm = lhs - other
                rhs = rhs - other
                diff = log(mainterm) - log(rhs)
                soln = _lambert(expand_log(diff), symbol)

    if not soln:
        raise NotImplementedError('%s does not appear to have a solution in '
            'terms of LambertW' % f)

    return list(ordered(soln))


def bivariate_type(f, x, y, *, first=True):
    """Given an expression, f, 3 tests will be done to see what type
    of composite bivariate it might be, options for u(x, y) are::

        x*y
        x+y
        x*y+x
        x*y+y

    If it matches one of these types, ``u(x, y)``, ``P(u)`` and dummy
    variable ``u`` will be returned. Solving ``P(u)`` for ``u`` and
    equating the solutions to ``u(x, y)`` and then solving for ``x`` or
    ``y`` is equivalent to solving the original expression for ``x`` or
    ``y``. If ``x`` and ``y`` represent two functions in the same
    variable, e.g. ``x = g(t)`` and ``y = h(t)``, then if ``u(x, y) - p``
    can be solved for ``t`` then these represent the solutions to
    ``P(u) = 0`` when ``p`` are the solutions of ``P(u) = 0``.

    Only positive values of ``u`` are considered.

    Examples
    ========

    >>> from sympy.solvers.solvers import solve
    >>> from sympy.solvers.bivariate import bivariate_type
    >>> from sympy.abc import x, y
    >>> eq = (x**2 - 3).subs(x, x + y)
    >>> bivariate_type(eq, x, y)
    (x + y, _u**2 - 3, _u)
    >>> uxy, pu, u = _
    >>> usol = solve(pu, u); usol
    [sqrt(3)]
    >>> [solve(uxy - s) for s in solve(pu, u)]
    [[{x: -y + sqrt(3)}]]
    >>> all(eq.subs(s).equals(0) for sol in _ for s in sol)
    True

    """

    u = Dummy('u', positive=True)

    if first:
        p = Poly(f, x, y)
        f = p.as_expr()
        _x = Dummy()
        _y = Dummy()
        rv = bivariate_type(Poly(f.subs({x: _x, y: _y}), _x, _y), _x, _y, first=False)
        if rv:
            reps = {_x: x, _y: y}
            return rv[0].xreplace(reps), rv[1].xreplace(reps), rv[2]
        return

    p = f
    f = p.as_expr()

    # f(x*y)
    args = Add.make_args(p.as_expr())
    new = []
    for a in args:
        a = _mexpand(a.subs(x, u/y))
        free = a.free_symbols
        if x in free or y in free:
            break
        new.append(a)
    else:
        return x*y, Add(*new), u

    def ok(f, v, c):
        new = _mexpand(f.subs(v, c))
        free = new.free_symbols
        return None if (x in free or y in free) else new

    # f(a*x + b*y)
    new = []
    d = p.degree(x)
    if p.degree(y) == d:
        a = root(p.coeff_monomial(x**d), d)
        b = root(p.coeff_monomial(y**d), d)
        new = ok(f, x, (u - b*y)/a)
        if new is not None:
            return a*x + b*y, new, u

    # f(a*x*y + b*y)
    new = []
    d = p.degree(x)
    if p.degree(y) == d:
        for itry in range(2):
            a = root(p.coeff_monomial(x**d*y**d), d)
            b = root(p.coeff_monomial(y**d), d)
            new = ok(f, x, (u - b*y)/a/y)
            if new is not None:
                return a*x*y + b*y, new, u
            x, y = y, x
